As an artist, I can understand the desire to be original. And, from what I've seen of your work, it is indeed unique. I believe, it was Pablo Picasso who said; "Good artist's borrow, Great artist's steal."
My point is, you can still build off others ideas, and add your own touch. Look at one of the most successful, and well-known incest games for instance, The Visit, Dreams of Desire, Milfy City..
I think the perfect incest game could be made using the blueprints of any of these games. Just customize using your style. Anyways, some of the things I find appealing in AVN's are:
*Footjobs
*Lingerie, Stockings, Heels
*Landlady with HUGE proportions
*Decent Story
*Love and Romance always good
*MC and Mom go on date
*Pregnancy option
I could go on and on. I thought of this one plot where the MC discovers his mom is a stripper. His friends take him to the strip club on his bachelor night. They make him wear a mask, his mom gives him a lap dance, and one thing leads to another. At the end she removes the mask and they are both shocked. Guy gets married, wife cheats on him, years later moves back in with his mom..
Good luck with your game, I'm glad to see a Dev creating a game in this genre.